The present invention relates to hydraulically powered exhaust gas recirculation systems for internal combustion engines.
Various turbochargers and super chargers are known in the art. In one type of turbocharger, the exhaust gas from the internal combustion engine drives a turbine, which in turn drives a compressor. The compressor pressurizes intake air and feeds it into the intake manifold of the internal combustion engine.
Exhaust gas recirculation (EGR) systems are sometimes used in conjunction with turbochargers. In such a system, a portion of the exhaust gas from the internal combustion engine is recirculated from the exhaust manifold back to the intake manifold. This reduces emissions from the engine to the atmosphere. In one system shown in WO 98/39563, published Sep. 11, 1998, a portion of the exhaust gas drives a turbine, which in turn powers a compressor. The compressor rotor has two sets of vanes on opposite sides of the rotor disk. In operation, one set of vanes pressurizes fresh intake air and delivers it to the intake manifold of the engine. A portion of the exhaust is also fed into the compressor, where it is pressurized by the other set of vanes and delivered to the intake manifold of the engine.
Another exhaust gas recirculation system is shown in U.S. Pat. No. 5,974,802 to Blake. In that system, a portion of the exhaust drives a turbine that in turn powers a compressor. The compressor pressurizes intake air, ultimately delivering it to the intake manifold of the engine. Another portion of the exhaust is pressurized by a coanda pump and ultimately delivered to the intake manifold of the engine.
In exhaust gas recirculation systems, the pressure of the fresh intake air is greater than the pressure of the recirculated exhaust gas. Accordingly, it is necessary to increase the pressure of the recirculated exhaust gas so that it will flow freely into the internal combustion engine. Although it is possible to introduce the recirculated exhaust gas into the engine""s fresh air inlet, exhaust gas can corrode components within the intake tract, such as the turbocharger compressor and the charge air cooler. It is possible to use throttling devices and venturi devices to lower the pressure in the intake tract to allow the recirculated exhaust gas to flow in the desired direction. However, the pressure losses associated with this technique create unacceptable energy losses in the engine. Thus, it is desirable to use a pump to raise the pressure of the recirculated exhaust gas such that flow into the intake tract is possible.
Obviously, it is necessary to provide an energy source to power the pump used to increase the pressure of the recirculated exhaust gas. Electric energy is impractical for this purpose. Various mechanical drive mechanisms are possible but have drawbacks. For example, slow speed compressors driven by the engine have many critical clearances which may be fouled by the exhaust gas. High speed centrifugal compressors require expensive drive systems to achieve the desired speeds. The exhaust gas itself can be utilized to drive a turbine, such as discussed above in conjunction with WO 98/39563. However, large amounts of power and high shaft speeds can be obtained by the use of hydraulic turbines in sizes smaller than the exhaust gas recirculation turbine of devices such as those shown in WO 98/39563. In an internal combustion engine, hydraulic power can be conveniently provided from either a dedicated pump driven by the engine or from an existing hydraulic source on the engine, such as power steering or fuel injection systems or an auxiliary hydraulic system.
The present invention is directed to a hydraulically powered exhaust gas recirculation system for an internal combustion engine. In one embodiment of the present invention, an exhaust gas recirculation system for a vehicle includes an internal combustion engine having an air inlet, a first turbine powering a first compressor, a second turbine powering a second compressor, and a hydraulic system. Exhaust from the engine drives the first turbine while the hydraulic system drives the second turbine. The first compressor delivers air to the engine inlet and the second compressor delivers exhaust from the engine to the inlet. The hydraulic system may include a power steering system, oil from a fuel injection system, a dedicated hydraulic pump or other devices. The system may also include coolers for cooling the air before it enters the engine inlet and the exhaust gas before it enters the second compressor. A mixer may be utilized to combine the air from the first compressor and the exhaust from the second compressor. The flow of exhaust to the engine may be regulated by any number of means, such as by a valve or through control of the hydraulic system.
It is an object of the present invention to provide an improved exhaust gas recirculation system for an internal combustion engine.
It is another object of the present invention to provide a hydraulically powered exhaust gas recirculation system for an internal combustion engine.